Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to vertical axis wind turbines, which are used to convert wind energy.
2. Description of the Related Art
The Darrieus-type vertical axis wind turbine, (VAWT) having its rotating shaft traverse to the air stream, was patented by G. M. Darrieus in the United States in 1931 U.S. Pat. No. 1,835,018. The Darrieus-type vertical axis wind turbine is said to resemble an egg-beater with curved blades connected at both ends to the ends of the rotating shaft. Each blade of the turbine is symmetrical in cross section and is curved in the shape of a perfectly flexible cable of uniform density and cross section would assume if spun about a vertical axis. This curved blade shape is represented by the Greek word xe2x80x9ctroposkeinxe2x80x9d meaning turning rope. With VAWT blades having a troposkein shape, major stresses are in tension when the rotor is spinning. Thus, rotation of the turbine rotor will not cause the blades to bend significantly nor to produce significant blade bending stresses.
The operational principal of the vertical axis wind turbine (VAWT) is an alogous to the aerodynamics of a wing (airfoil) as is described in xe2x80x9cThe Wind Power Bookxe2x80x9d pages 78 and 79 by Jack Park. Fluid forces on the blades of the VAWT are divided into lift and drag forces. A component of the lift force causes rotor rotation and a component of the drag force opposes rotor rotation. The rotor torque will be positive as long as the driving component of the lift force exceeds the opposing component of the drag force. With such a rotor the aerodynamic efficiency is low or negative at rotor tip speed over wind speed ratios below 3 or above 9. Consequently, a motor must usually be employed to start the turbine.
Interest in the Darrieus-type vertical axis wind turbines has been stimulated in recent years by the energy crisis and the important advantages of such turbines over horizontal axis machines which include the following: (1) The VAWT accepts wind from all directions and therefore does not require costly direction orientating equipment. (2) The VAWT does not require adjustment of blade pitch to limit maximum power output at high wind speeds. (3) The generator, speed reducer and brake do not have to be supported as part of the wind orientating platform. (4) The VAWT blades are supported at both ends which makes for less expensive and longer lasting blades.
VAWT designs have advanced and have inherent advantages over horizontal axis machines. But a VAWT is needed to be more cost effective in construction, erection, maintenance and operation.
Inventors have made attempts to create a VAWT that will prosper with the stable energy price following the panic of 1973.
U.S. Pat. No. 5,252,029 to Barnes discloses a VAWT having both an erection and hold down gin poles that allow pivot erection using a ground mounted winch. These gin poles provide tension reduction for the erection and hold down cables that hold the turbine together during pivot erection. This disclosure only describes two assembly cables. This disclosure only accounts for forces and movement in the plane containing the two cables and the major axis of the VAWT rotor shaft. The drawings in this disclosure show alignment between the major axis of the drive train frame and the major axis of the rotor shaft.
Forces and rotor shaft movement may develop in other planes. The plane, at right angles to the two cables and rotor shaft axis plane, is the plane where extra forces and rotor movement is most likely. These extra forces and rotor movement will occur due to the rolling of the cables in the gin pole guide cups causing misalignment. Once the rotor axis starts to leave the drive train frame axis plane, right angle plane forces increase. This movement and right angle plane force increase could cause rotor bearing damage. This rotor shift, during erection, could limit rotor length and therefore energy conversion rating.
In accordance with the present invention a vertical axis wind turbine assembly is connected by a hinge to a ground embedded anchor. The turbine assembly is assembled in a horizontal position close to the ground. This turbine assembly is held together by the three upper bearing guy cables. One guy cable is strung over an erection gin pole and connected to an anchor mounted winch. The other two guy cables are strung over a combined hold down and stabilizing T-shaped pole to hold together and align the assembly during pivot erection to a vertical position.
The objects and advantages of this invention are:
A. To provide a vertical axis wind turbine design with improved overall cost effectiveness, particularly construction and installation cost.
B. To provide a cost effective vertical axis wind turbine design for turbines of practical commercial and industrial power conversion ratings.
C. This cost effective VAWT must also survive high winds while in a fully installed condition.
D. This cost effective VAWT design must also inhibit rotor torque ripple, guy cable vibration and rotor blade fatigue. The objects of this invention have been obtained with three principal advantages over previous vertical axis wind turbine designs:
1. An additional set of guy cables to hold the central support structure and lower rotor bearing in a vertical position. This central support structure guy cable set reduces the cost of the central support structure. The central support structure principally consists of the drive train frame.
2. Pivoting the entire turbine, except the central support structure anchor, during erection. This invention pivots the support structure and rotor lower bearing also the rotor shaft and rotor upper bearing assembly from a horizontal to a vertical position. The turbine single axis pivot pin or pins are mounted close to the ground in a central support structure anchor. This central support structure anchor is embedded in the ground.
3. The use of erection and combination hold down and stabilizing gin poles combined with a low erection pivot axis allows for turbine erection without an expensive tall crane. The turbines of this invention have been sized (10 horsepower, 25 HP. 50 HP. and 75 HP.) and designed to allow cable pivoting using a ground mounted winch.
Additional design features of this invention are:
1. A flexible rotor shaft to speed reducer shaft coupling. This shaft coupling has replaceable flex elements to reduce rotor torque ripple. This shaft coupling reduce rotor blade, rotor shaft and speed reducer fatique.
2. A simple inexpensive guy cable vibration dampening device installed in each upper rotor bearing cable. These cable vibration devices reduce cable vibration and cable tension and therefore rotor bearing wear.
3. Conservative sizing of guy cables for withstanding high winds with turbine fully installed.
4. A spring set electrically released emergency stop and parking brake is used. This brake is sized and engaged to stop the turbine rotor in high winds.
5. The low pivot erection axis allows the use of inexpensive low lift equipment for turbine component assembly. This low pivot axis reduces turbine maintenance costs.
6. The rotor shafts, rotor blade hubs, rotor blades and blade connections have been sized and designed to withstand rotor run away in high winds.
7. The practical size of the turbines of this invention allows for cost effective adaptation of standard industrial components. These standard components are tapered roller bearings, in-line gearboxes, induction motor generators, steel and aluminum pipe, plate and beams.
8. Contoured fit blade clamps, used with slotted mounting holes, helps reduce rotor blade stress due to flatwise modal vibration.
9. Specially designed extruded hollow aluminum beams that can be easily machined and bolted together to form blade hubs. Bolted blade hubs avoids the cost of welding. Still further turbine features and advantages will become apparent from consideration of the ensuing descriptions and drawings.